feat(openai): support deferred resolution for configured MCP connectors

[mkoushni]

Summary

Praxis connector_id values are pipeline-local. Accepting defer_loading: true without an ownership model would have forwarded those IDs to the inference backend.

• openai_mcp_tool_resolve accepts deferred configured connectors when the request includes tool_search, injects the configured URL in-memory only, skips eager tools/list, and rewrites the backend body to a sanitized type: mcp stub (no connector_id, URL, authorization, or headers).
• openai_agentic_loop extracts tool_search_call into request state (not backend messages).
• openai_mcp_dispatch loads every pending deferred connector on tool_search_call, then dispatches through the existing tools/call path.
• Discovery is transactional: list all connectors first, then apply name-collision and max_rewritten_body_bytes checks before mutating mcp_tool_map or output. Failures restore pending connectors.
• Unknown IDs and connector_id + server_url still 400 before outbound activity. Eager connectors and direct server_url are unchanged.

The first inference round still sends the sanitized type: mcp stub plus tool_search; the backend must accept those OpenAI hosted-tool shapes. Any tool_search_call loads every pending deferred connector.

Closes #703

Validation

• cargo test -p praxis-ai-apis --lib -- openai_mcp_tool_resolve agentic_loop mcp_dispatch (316 passed)
• cargo test -p praxis-tests-integration --test suite -- deferred_connector mixed_eager (5 passed)
• cargo clippy -p praxis-ai-apis --all-targets -- -D warnings
• make lint

Checklist

• I reviewed every changed line and can explain the change.
• New capabilities include an example config and functional example test.
• User-facing behavior and generated documentation are updated.
• Commits are signed and include a Signed-off-by trailer.

Breaking changes

None. Deferred connector_id was previously rejected; it is now accepted only with tool_search and an agentic MCP dispatch loop.

[praxis-bot-app]

Missing Signed-off-by: 8998839. All commits require sign-off (via git commit --signoff).